The present invention relates to an ion source for use in a mass spectrometer and, more particularly, to an ion source which can directly introduce liquid sample into the ionization chamber to ionize it by electron-impact ionization or chemical ionization.
Various systems have been heretofore proposed to introduce eluate from a liquid chromatograph into a mass spectrometer, for analyzing the eluate. For example, a system using a moving belt is disclosed in U.S. Pat. No. 4,055,987. A direct inlet system employing a nozzle is proposed in U.S. Pat. No. 4,298,795.
In the former system, column eluate is dropped onto a belt under atmospheric pressure and carried into the ionization chamber. The belt is heated to vaporize the solute, which is then ionized. This system needs a large-scale differential pumping system to permit the belt to be carried into the ion source. Further, it is difficult to eliminate a so-called memory effect due to residues on the belt.
In the latter system, a nozzle is used to directly spray column eluate into the ionization chamber. The vaporized solute is ionized. Since the nozzle is complex and delicate, it clogs easily. Hence, it is difficult to stably introduce the solute into the ionization chamber.